Microscale metallic CNT templated devices and related methods

ABSTRACT

A method for forming a microscale device may include growing, by a chemical vapor deposition, a patterned forest of vertically aligned carbon nanotubes, wherein the patterned forest defines a component of the microscale device, and applying a conformal non-metal coating to the vertically aligned carbon nanotubes throughout the patterned forest, wherein the conformal non-metal coating comprises a substantially uniform thickness along a length of the vertically aligned carbon nanotubes. The method may also include connecting adjacent vertically aligned carbon nanotubes together with the conformal non-metal coating without filling interstices between the adjacent vertically aligned carbon nanotubes, wherein the connecting of the vertically aligned carbon nanotubes is configured to increase a strength of the vertically aligned carbon nanotubes of the patterned forest above a threshold level to withstand forces applied during a wet etching process, and infiltrating the interstices between the adjacent vertically aligned carbon nanotubes with a metallic material.

PRIORITY CLAIMS

This application is a continuation of U.S. patent application Ser. No.15/723,004, filed Oct. 2, 2017, which is a continuation of U.S. patentapplication Ser. No. 13/657,678, filed Oct. 22, 2012, which claimspriority to U.S. Provisional Patent Application No. 61/627,919, filedOct. 20, 2011. The aforementioned applications are incorporated hereinby reference as if fully set forth.

BACKGROUND

The present invention relates generally to three-dimensional microscalestructures and methods relating to the formation of such structures.

Precision manufacturing of three-dimensional structures on themicroscale is of great interest in a variety of sensing and relatedapplications. At present, however, such endeavors have been limited torelatively low aspect ratio devices and to a narrow range of materials.Metals and metal alloys are commonly used in larger applications, buthave faced significant barriers at the microscale level.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop highaspect ratio, three-dimensional microscale structures from metals tometal alloys.

In accordance with an aspect of the present disclosure, a microscaledevice is disclosed. The microscale device may include a patternedforest of vertically grown and aligned carbon nanotubes defining acarbon nanotube forest with the nanotubes having a height defining athickness of the forest. The patterned forest may define a patternedframe that defines one or more components of the microscale device. Themicroscale device may also include a conformal coating of substantiallyuniform thickness extending throughout the carbon nanotube forest. Thecarbon nanotube forest may have a thickness of at least three microns.The conformal coating may substantially coat the nanotubes, definecoated nanotubes and connect adjacent nanotubes together such that thecarbon nanotube forest is sufficiently robust for liquid processing,without substantially filling interstices between individual coatednanotubes. The microscale device may also include a metallicinterstitial material infiltrating the carbon nanotube forest and atleast partially filling interstices between individual coated nanotubes.

At least one component of the patterned frame may be fixed and at leastone component of the patterned frame may be moveable relative to thefixed component. The metallic interstitial material may be applied by anelectroplating process. The metallic interstitial material mayinfiltrate the carbon nanotube forest with an infiltration uniformityachieved by application of the electroplating process to the carbonnanotube forest.

The conformal coating may include a carbon material. The metallicinterstitial material may include nickel.

The thickness of the carbon nanotube forest may be between 3 μm(microns) and 9 mm. The microscale device may include amicroelectromechanical systems (MEMS) device.

The microscale device may define at least a portion of a sensor. Thesensor may include a gyro. The gyro may include a transductive capacitorthat includes a capacitive gap in the form of a trench defined by themicroscale device. The trench may include a height-to-width ratio of atleast 100:1.

In accordance with another aspect of the present disclosure, amicroscale device is disclosed. The microscale device may include apatterned forest of vertically grown and aligned carbon nanotubesdefining a carbon nanotube forest with the nanotubes having a heightdefining a thickness of the forest. The patterned forest may define apatterned frame that defines one or more components of the microscaledevice. The carbon nanotube forest may include at least one featureincluding a height-to-width ratio greater than 100:1. The microscaledevice may also include a conformal coating of substantially uniformthickness extending throughout the carbon nanotube forest. The carbonnanotube forest may have a thickness of at least three microns. Theconformal coating may substantially coat the nanotubes, define coatednanotubes and connect adjacent nanotubes together, without substantiallyfilling interstices between individual coated nanotubes. The microscaledevice may also include a metallic interstitial material infiltratingthe carbon nanotube forest and at least partially filling intersticesbetween individual coated nanotubes.

At least one component of the patterned frame may be fixed and at leastone component of the patterned frame may be moveable relative to thefixed component. The microscale device may define at least a portion ofa gyro that includes a transductive capacitor. The feature may include acapacitive gap in the form of a trench defined by the microscale device.

The feature may include a height-to-width ratio greater than 200:1. Themetallic interstitial material may be applied by an electroplatingprocess. The metallic interstitial material may infiltrate the carbonnanotube forest with an infiltration uniformity achieved by applicationof the electroplating process to the carbon nanotube forest.

The conformal coating may include a carbon material. The metallicinterstitial material may include nickel.

In accordance with another aspect of the present disclosure, amicroscale device is disclosed. The microscale device may include apatterned forest of vertically grown and aligned carbon nanotubesdefining a carbon nanotube forest with the nanotubes having a heightdefining a thickness of the forest. The patterned forest may define apatterned frame that defines one or more components of the microscaledevice. The microscale device may also include a conformal coating ofsubstantially uniform thickness extending throughout the carbon nanotubeforest. The carbon nanotube forest may have a thickness of at leastthree microns. The conformal coating may substantially coat thenanotubes, define coated nanotubes and connect adjacent nanotubestogether, without substantially filling interstices between individualcoated nanotubes. The microscale device may also include a metallicinterstitial material infiltrating the carbon nanotube forest and atleast partially filling interstices between individual coated nanotubes.The metallic interstitial material may infiltrate the carbon nanotubeforest with an infiltration uniformity achieved by application of anelectroplating process to the carbon nanotube forest.

The infiltration uniformity may be achieved by application of a pulsedcurrent. The carbon nanotube forest may include at least one featureincluding a height-to-width ratio greater than 100:1.

At least one component of the patterned frame may be fixed and at leastone component of the patterned frame may be moveable relative to thefixed component. The microscale device may define at least a portion ofa gyro that includes a transductive capacitor. The feature may include acapacitive gap in the form of a trench defined by the microscale device.

The conformal coating may include a carbon material. The metallicinterstitial material may include nickel.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIG. 1A is an SEM image of an exemplary block of material created usingthe present technology:

FIG. 1B is an SEM image of various silicon nitride structures for use asor in MEMS devices, the silicon nitride structures fabricated using anitride carbon nanotube templated microfabrication (CNT-M) process inaccordance with an embodiment of the invention;

FIG. 1C is an SEM image of a freestanding MEMS device in accordance withan embodiment of the invention;

FIGS. 2A through 2E illustrate various steps in a process of creating anMEMS device in accordance with an embodiment of the invention;

FIGS. 3A through 3D illustrate various steps in a process of filling apatterned CNT forest in accordance with an embodiment of the invention;

FIG. 4A is an SEM image of an electrodeposition into a CNT-M foresttemplate;

FIG. 4B is an SEM image of a broken feature showing internal filling ofthe structure in accordance with an embodiment of the invention;

FIGS. 5A through 5H illustrate various steps of utilizing a sacrificiallayer to define a sense gap in an exemplary MEMS structure in accordancewith an embodiment of the invention;

FIG. 6 is a schematic illustration of an exemplary remote sensing unitutilizing microscale devices in accordance with the present inventionfor use in extreme sensing conditions.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

In describing and claiming the present invention, the followingterminology will be used.

As used here, the term “vertically grown” is used to describe nanotubesthat are generally grown upward from a substrate or catalyst material.While such nanotubes exhibit a generally vertical attitude, it is to beunderstood that such tubes are not necessarily perfectly straight orperfectly upright, but will tend to grow, twist or otherwise meanderlaterally to some degree, as would be appreciated by one of ordinaryskill in the art.

As used herein, the term “aligned” is used to describe nanotubes thatgenerally extend in a common direction from one side or surface toanother. While such nanotubes exhibit a generally or substantialalignment, it is to be understood that such tubes are not necessarilyperfectly straight or perfectly aligned, but will tend to extend, twistor otherwise meander laterally to some degree, as would be appreciatedby one of ordinary skill in the art. In describing and claiming thepresent invention, the following terminology will be used.

As used herein, the term “patterned frame” is to be understood to referto a framework or latticework or grate that includes an often planarbase and an often planar face with constituent materials of thepatterned frame arranged laterally relative to, and generally beginningor terminating at, the base and the face of the patterned frame. In mostcases, the patterned frame will include one or more laterally extendingwalls that define, circumscribe or surround one or more passagesextending through the frame from the base of the frame to the face ofthe frame.

One non-limiting example of a patterned frame in accordance with oneaspect of the present invention is a grate structure having a repeatingpattern of a plurality of intersecting walls that define a plurality ofequally shaped and spaced passages. These passages are typically on themacro scale compared to the spacing between, and size of, the carbonnanotubes used in the present structures.

As used herein, the term “passage” refers to an opening or a void formedin a patterned frame by the carbon nanotubes that define or constitutethe frame. A passage can be completely devoid of material, or it can befilled, or partially filled, with an interstitial or conformal material.Oftentimes, the internal walls of the passages are at least covered orcoated by the conformal or interstitial material.

As used herein, the term “microscale device” is used to describe devicesthat include features sized in the range of a few microns up to hundredsof microns. While an overall device may be very large (millimeters andlarger), microscale devices may be used as one or more components thatcollectively make up the overall device.

As used herein, relative terms, such as “upper,” “lower,” “upwardly,”“downwardly,” “vertically.” etc., are used to refer to variouscomponents, and orientations of components, of the systems discussedherein, and related structures with which the present systems can beutilized, as those terms would be readily understood by one of ordinaryskill in the relevant art. It is to be understood that such terms arenot intended to limit the present invention but are used to aid indescribing the components of the present systems, and related structuresgenerally, in the most straightforward manner. For example, one skilledin the relevant art would readily appreciate that a “vertically grown”carbon nanotube turned on its side would still constitute a verticallygrown nanotube, despite its lateral orientation.

As used herein, the term “interstitial” material is used to refer to amaterial that at least partially fills interstices, or small spaces,between or in individual nanotubes that form an array or forest ofnanotubes.

As used herein, the term “interlocked” is to be understood to refer to arelationship between two or more carbon nanotubes in which the nanotubesare held together, to at least some degree, by forces other than thoseapplied by an interstitial coating or filling material. Interlockednanotubes may be intertwined with one another (e.g., wrapped about oneanother), or they may be held together by surface friction forces, vander Waals forces, and the like.

When nanotubes are discussed herein as being “linearly arranged” or“extending linearly,” it is to be understood that the nanotubes, whilepossibly being slightly twisted, curved, or otherwise meanderinglaterally, are generally arranged or grown so as to extend lengthwise.Such an arrangement is to be distinguished from nanotubes that arerandomly dispersed throughout a medium.

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. As an arbitrary example, when anobject or group of objects is/are referred to as being “substantially”symmetrical, it is to be understood that the object or objects areeither completely symmetrical or are nearly completely symmetrical. Theexact allowable degree of deviation from absolute completeness may insome cases depend on the specific context. However, generally speakingthe nearness of completion will be so as to have the same overall resultas if absolute and total completion were obtained.

The use of “substantially” is equally applicable when used in a negativeconnotation to refer to the complete or near complete lack of an action,characteristic, property, state, structure, item, or result. As anarbitrary example, an opening that is “substantially free of” materialwould either completely lack material, or so nearly completely lackmaterial that the effect would be the same as if it completely lackedmaterial. In other words, an opening that is “substantially free of”material may still actually contain some such material as long as thereis no measurable effect as a result thereof.

Precision manufacturing of three-dimensional structures on themicroscale is central to a variety of sensing and other applications. Atpresent, however, such manufacturing is limited to relatively low aspectratios and to a narrow range of materials. Metals and metal alloys arecommonly used at other length scales but have faced significant barriersat the microscale.

The present invention can be applied to a variety of microscale devicesand microelectromechanical systems (MEMS). While the technology can beapplied to myriad applications, some specific examples of variousdevices are described herein. For example, inertial sensing is oneparticular application that could significantly benefit from thefabrication of metal and metal alloys precisely structured intothree-dimensional shapes. The present invention provides atransformative process for fabrication of high aspect ratio,three-dimensional microscale structures from metals and metal alloys.These structures are sometimes referred to herein as metal carbonnanotube templated microfabrication (metal CNT-M) structures.

MEMS-based inertial sensing of acceleration and rotation is widely usedin automotive, industrial, defense, aerospace, medical, and mobiledevices. Despite this widespread success, however, current MEMS inertialsensors are limited to fabrication in a narrow range of materials and atrelatively low aspect ratios. Sensor fabrication to date has primarilybeen accomplished by bulk and surface silicon micromachining withcommercial sensors primarily fabricated using surface techniques.

In inertial sensing, capacitive transduction is the chief detectionmechanism. Aspect ratio (the ratio of height to gap width) is the mainparameter determining the sensitivity of capacitive transduction;increasing aspect ratio increases transduction sensitivity. High aspectratios also provide high out-of-plane mechanical stiffness whichisolates sensing of motions in one direction from parasitic motions inother directions, and is desirable in many of the compliant mechanismsused in MEMS sensing and actuation. Deep reactive ion etching canproduce aspect ratios up to 50:1 in micromanufactured siliconstructures: however, there is no corresponding metals etching technologycapable of producing high aspect ratios.

A major inertial sensing challenge is precision measurement of rotationfor navigation. This is a demanding application which requires highsensitivity and low drift. Angular bias drift requirements fornavigation can be as stringent as 0.001 degrees per hour. Current MEMSgyros fall far short of this requirement. MEMS gyros operate byresonating a proof mass and capacitively detecting the effects ofrotation induced coriolis forces on the resonator. On the hardware side,gyro sensitivity and stability are determined by two main factors: thecharacteristics of the mechanical resonance and the geometry of thecapacitive sensing surfaces. Higher aspect ratios in the capacitancesensing gap directly yields higher capacitance sensitivity and improveddrift performance. Drift performance is also improved by increasing theresonator decay time constant. Current silicon MEMS gyro fabricationtechniques yield aspect ratios around 20:1 and bias drift and yield biasstabilities around 1 degree per hour, about 1000 times too low for themost demanding navigation applications.

Many three-dimensional MEMS structures to date have been produced bydeep silicon reactive ion etching (DRIE). However, the difficulty inproducing extremely high aspect ratio structures (or even moderateaspect ratios in metals) by deep etching has led to the use of alternatefabrication process, such as that known as LIGA. In this process, anegative of the pattern is made and the material (usually anelectroforming or moldable material) is filled into the gaps. LIGA inits original form, however, requires the use of a synchrotron radiationsource. To be cost effective, a mold needs to be formed and used manytimes. LGA-like processes using SU-8 have been demonstrated using moreconventional lithography. These LIGA-like processes achieve smalleraspect ratios and shorter structures than true LIGA. Additionally. LIGAand LIGA-like processes for fabrication of structures with high aspectratios rely on electrodeposition of metal layers that are very thickresulting in very high stresses. These stresses result in significantdistortions even for relatively thin electrodeposited layers.

The present invention can produce feature dimensions similar to thoseachieved by LIGA processes: feature widths and gaps of several micronsand heights of hundreds to thousands of microns resulting in extremelyhigh aspect ratios. The present technology, however, provides somesignificant advantages over LIGA particularly in the thinness of theelectroplating and in cost. The present electroplating process canutilize a carbon nanotube scaffolding as the electrode, such that theplating proceeds from each nanotube and only needs to proceed until itcontacts the coating from the neighboring nanotube. Thus, the requiredelectroplating thicknesses are small even for very tall features,resulting in distortion-free high aspect ratio features.

Typically, film stress (and corresponding distortion) increases withincreased plating thickness: thus, the present thin plating utilized inthe present technology provides a significant advantage. In addition,the costs associated with the present technology are much lower thanconventional methods. The present technology can utilize inexpensive andreadily available lithography. CVD, and electroplating processes.

The present technology provides for fabrication of high aspect ratioMEMS and other three-dimensional microstructures from many differentmaterials including (but not limited to) silicon and silicon nitride,silicon dioxide, carbon, and metals. FIGS. 1A-1C illustrate variousstructures created using the present technology. FIG. 1A is an SEM imageof an exemplary 3 μm pitch grid pattern grown to 580 μm in height. FIG.1B is an SEM image of various silicon nitride structures fabricatedusing a nitride CNT-M process in accordance with one exemplaryembodiment of the invention. FIG. 1C is an SEM image of freestandingcarbon infiltrated CNT-M cell gripper device: one of various MEMSstructures that can be created using the present invention.

FIG. 2 illustrates an exemplary process for carbon nanotube-templatedmicrofabrication (CNT-M) of MEMS. In this embodiment, a thin catalysislayer (iron on alumina typically) can be deposited on a substrate andpatterned (see FIG. 2A). After this, nanotube growth can be initiated byvarious manners described herein or in preceding applications to thepresent inventors (see FIG. 2B). At FIG. 2C, the nanotube forest can befilled (from a partial coating on the nanotubes to nearly solid fillingof the structure) using techniques such as CVD or an aqueous liquidelectroplating process or combinations of these processes. At FIG. 2D,any potential “floor layer” that is a byproduct of some to theinfiltration processes (but not all) can be etched, and at FIG. 2e theunderlying layer can be etched, resulting in both attached andfree-standing structures. This process can be utilized to create avariety of MEMS structures, as would be readily appreciated by one ofordinary skill in the art having possession of this disclosure.

The present inventors have developed a CNT-M process for fabrication ofhigh aspect ratio MEMS and other three-dimensional microstructures frommany materials. The nanotubes grown (shown for example in FIG. 2B) canbe grown to over 500 microns in height, with lateral pattern dimensionsdown to 2-3 microns. In this manner, the aspect ratios in the gapsformed can be greater than 200:1. Based on a very low edge roughness(100 nm), gap spacing can be reduced even further using improved butbasic lithography only to 1 μm or below, further increasing aspectratio.

Despite the solid appearance of the CNT structures prior to infiltration(see, e.g., FIG. 1A), the vertically aligned carbon nanotube material istypically very low density (less than 1% solid by volume) andmechanically very weak. The degree of infiltration of the nanotubetemplate can be variable from a nearly solid structure to very limited,resulting in a porous structure. The nearly solid structures haveproperties that are very similar to the infiltration material. One keyfeature of the low degree of infiltration processes is that theindividual nanotubes are linked up to the neighboring nanotubes giving astructure that is sufficiently strong to be handled and placed inliquids without destroying the framework.

FIG. 3 illustrates low pressure chemical vapor deposition (LPCVD)infiltration of silicon into patterned CNT forests. This is a typicalexample of the infiltration processes that can be utilized. At 3A, aschematic of the radial filling process is provided, with some voidsremaining in the composite. 3B includes an SEM image showing the outsideof an as-grown forest. The dotted box in the inset indicatesschematically the location of the image on a wall of nanotubes. Scalebar 500 nm, 50° tilt. At 3C, the outer wall of the forest is shown afterfilling with silicon. Scale bar 500 nm, 50° tilt. Inset shows thelocation of the image. At 3D, a cleaved cross-section of asilicon-filled forest is provided. This image was taken at 50° tilt.Scale bar 1 μm. The dotted box in the inset indicates the location ofthis image.

The infiltration can come from a variety of processes depending upon thedesired infiltration material. For silicon and silicon nitride, lowpressure chemical vapor deposition (LPCVD) can be used. For carbon, CVDcan be done at atmospheric pressure. For metals, CVD processes orelectroplating can be used. One challenge in infiltration is tuning thebasic deposition processes to coat the nanotubes conformally anduniformly in order to achieve high fill density. The ideal conditionsresult in growth rates limited by surface kinetics rather than masstransport of reactants to and from the growth sites. When transport ofreactants dominates the process, the coating is on the outside of thenanotube form while when surface kinetics dominates the coating isuniform throughout the structure. In between these extremes, theinfiltration is dependent on distance from exposed surfaces, and tuningthe geometry of the structure can be important.

While in one aspect of the invention the CNT-M process can be carriedout using ceramics (silicon, carbon and silicon nitride, etc.), in otheraspects a metal or metal alloy can be utilized. For example, in oneembodiment, electroplating with nickel was used to infiltrate CNT foresttemplates. Prior to electroplating, a thin carbon infiltration can beperformed to link the nanotubes together and make the CNT forest orframe sufficiently robust for liquid processing. Pulsed currentelectroplating can be performed to uncouple the depositing of metalduring current flow (surface reactions) from the mass transport ordiffusion of reactants into the forest. In one example a nickelsulfamate/nickel chloride electroplating bath was used at 40° C. FIGS.4A and 4B include SEM images of grid patterns formed in this manner withabout 2-micron-wide features. One of ordinary skill in the art willappreciate from these figures that very good infiltration uniformity canbe achieved at this feature size. Much larger features may requiredifferent pulse plating conditions and possibly spaced access holes forincreased ion transport. However, such features can be readilyincorporated into the present invention.

In one exemplary aspect of the invention, metal CNT-M MEMS structurescan be created for use in sensing applications (e.g., transductivecapacitors and the like). Generally, capacitive transduction sensitivityincreases as the inverse of gap size so very small gaps betweenresonator and sense electrodes are desirable. This typically requireshigh vertical sidewall straightness and low sidewall roughness. Highaspect ratio pores (over 200:1) have been fabricated by the presentinventors using CNT-M due to the excellent straightness and low surfaceroughness of the pore walls. The present technology achieves trenchaspect ratios of least 100:1 using the CNT-M process illustrated in FIG.2. Trench structures may have different achievable aspect ratios thanpore structures, as CNT forest features are not locally connected acrossthe trench. Thus, trench structures may require a higher inherent growthverticality.

Much higher aspect ratios can be achieved by extending the CNT-M processto define the vertical capacitive sensing gap between the resonator andthe detection electrodes by adding a sacrificial layer on anelectropolished sense electrode and then using the sacrificial layer to“template” the capacitive gap. This process can proceed as shown in FIG.5. Both organic and inorganic sacrificial layers can be utilized toproduce layers that have both high uniformity and highly selective etchrates relative to nickel.

The phases depicted in FIG. 5A through 5H illustrate one exemplarymanner in which very small gaps can be formed between components of adevice. The process can proceed as follows: at 5A, VACNT forests can begrown on a catalyst pattern defining resonator and sense electrode. At5B, brief deposition of carbon on the VACNT can be used to tie CNTstogether, making the frame sufficiently robust for wet processing. Anoxygen plasma etch step can be used to remove the floor layer,electrically isolating the resonator and sensing electrodes. At 5C, thesensing electrodes can be electrically connected to the plating powersupply and plated.

At 5D, electropolishing can be used to smooth the “sense” electrodesurface. At 5E, a sacrificial layer can be electrodeposited or grown onthe sense electrode surface. At 5F, the surface of the sacrificial layercan be seeded and electroless plated (if needed) to make the surfaceconductive. At 5G, nickel plating can form the resonator. Solid surfaceof the sacrificial layer can provide a flat non-porous surface totemplate smooth outer nickel surface on the resonator. At 5H, mechanicalpolishing can be used to expose the top edge of the sacrificial layerand the sacrificial layer can be selectively etched until removed.

Various other microscale- or MEMS-sensing devices can be provided inaccordance with other aspects of the invention. For example, sensing inextreme environments can be enabling for a wide variety of applications,including several in the energy industry. One area of sensing for energyapplications is acceleration sensing in high temperature, highacceleration, and corrosive environments. These include the environmentsin turbines used in both aircraft and ground based power generationsystems. Exploration for oil and drilling for carbon sequestration canalso benefit from vibration sensing in the high temperature and highacceleration environment of a drilling head. The present technology canbe utilized to provide a class of remotely detectable wireless passivemicroscale or MEMS acceleration sensors based on structures that arestable in high temperature (at least 100° C. and potentially over 1400°C.) environments.

As an example, as illustrated in FIG. 6, in one embodiment of theinvention a remote sensing unit can be provided that can contain anantenna attached to an MEMS capacitive acceleration sensor. Vibrationscan produce shifts in the sensor unit's microwave resonance, and thereader unit can detect the resonance changes by exciting the sensingunit with microwave radiation and detecting the reflected radiation(essentially, using radar).

While the discussions herein focus primarily on vibration sensing, lowfrequency and constant acceleration can also be detectable by thisdevice. The sensor technology can also be adaptable to a wide variety ofsensing challenges including measurements of sound pressure gradients,temperature, and chemical sensing. The present technology can addressthe following sensor fabrication challenges not heretofore accomplished:the sensors can be fabricated from materials that are stable in the hightemperature environments they will be probing. The sensor structures canbe fabricated from metals with high conductivity to achieve highsensitivity. High aspect ratio structure can be provided for highout-of-plane mechanical stiffness and high capacitance sensitivity,resulting in a sensor with less cross-talk and higher resolution.

These fabrication challenges can be met using a rapid, facile carbonnanotube template microfabrication (CNT-M) process that allows formicrofabrication of high aspect ratio structures from a variety ofrefractory metals, including, without limitation, tungsten, nickel, andplatinum.

In one embodiment of the invention, the sensor can operate on theprinciple of scattering of far-field radiation emitted by a readerantenna. The emitted radiation can be reflected by the sensor antenna,and can be sensed by either the reader antenna itself or by a thirdantenna located near the emitting antenna. The sensor antenna'sreactance can be modified by the sensed signal. In this case,acceleration of the movable mass can change the capacitance attached tothe sensor antenna. This modified reactance changes the resonantfrequency and quality factor for the radiation reflected by the sensorantenna, resulting in a change of the radar cross section of the sensor.The reader antenna can either perform a frequency sweep to find thesensor antenna's resonant frequency, or it can read changes in the radarcross section at a discrete number of frequencies.

One advantage of this wireless sensing technique, compared for instanceto inductive coupling, is increased range. For this reason, a verysimilar technique is used for many passive RFID tags, resulting in atypical read range of several (3-20) meters (depending on the gain ofthe reader antenna). However, unlike RFID tags, the sensor requires nodigital electronics or wiring at the sensing location, since theelectronics would be unlikely to survive for long periods at hightemperature. The sensor also operates without a battery, which isimportant both for high temperatures and for long-term operation. Thedownside, as with RFID tags, is that relatively high read power (about 1W) is required for reading the sensor. Assuming that the sensor uses adipole antenna, a relatively simple model can be used to predict theresonant frequency changes in response to acceleration.

Returning to FIG. 1C, one of a myriad of MEMS structures that can beformed using the present technology is illustrated. In this instance, aMEMS device 10 is provided that can serve as a gripping device. Thegripping device can include base members 12 that will be anchoredstationary relative to various moving components. Grip arms 14 moverelative to the base members in response to actuation applied to leverarm 16. While the mechanics of this simple example are relativelystraightforward, the process for providing MEMS devices on the presentscale and formed of the present materials have proved prohibitivelydifficult in past endeavors.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

The invention claimed is:
 1. A method, comprising: growing, by achemical vapor deposition, a patterned forest of vertically alignedcarbon nanotubes, wherein the patterned forest defines a component of amicroscale device; applying a conformal non-metal coating to thevertically aligned carbon nanotubes throughout the patterned forest,wherein the conformal non-metal coating comprises a substantiallyuniform thickness along a length of the vertically aligned carbonnanotubes; connecting adjacent vertically aligned carbon nanotubestogether with the conformal non-metal coating without fillinginterstices between the adjacent vertically aligned carbon nanotubes,wherein the connecting of the vertically aligned carbon nanotubes isconfigured to increase a strength of the vertically aligned carbonnanotubes of the patterned forest above a threshold level to withstandforces applied during a wet etching process; and infiltrating theinterstices between the adjacent vertically aligned carbon nanotubeswith a metallic material.
 2. The method of claim 1, wherein theconformal non-metal coating is a silicon or silicon nitride.
 3. Themethod of claim 1, wherein the conformal non-metal coating is a ceramicmaterial.
 4. The method of claim 1, wherein the metallic material isnickel.
 5. The method of claim 1, wherein a height of the verticallyaligned carbon nanotubes are between 3 microns and 9 microns.
 6. Amethod, comprising: growing a patterned forest of intertwined carbonnanotubes, wherein the patterned forest comprises: a first portiondefining a first component of a microscale device; and a second portiondefining a second component of the microscale device; applying aconformal non-metal coating to the intertwined carbon nanotubesthroughout the patterned forest, wherein the conformal non-metal coatingcomprises a substantially uniform thickness; infiltrating the patternedforest with a first interstitial material that is different than thenon-metal coating, wherein the first interstitial material at leastpartially fills interstices between the intertwined carbon nanotubes;applying a sacrificial layer over the first portion of the patternedforest; and electrodepositing a second interstitial material on thesecond portion of the patterned forest.
 7. The method of claim 6,further comprising electrically isolating the first component of themicroscale device and the second component of the microscale device,wherein: the first component is a resonator of a microscale sensingdevice, wherein the resonator is configured to sense a change inresonant frequency; and the second component is a sense electrode of themicroscale sensing device.
 8. The method of claim 7, further comprisingelectropolishing the second component prior to applying the sacrificiallayer to increase the sensing of the microscale sensing device.
 9. Themethod of claim 6, wherein the sacrificial layer is deposited betweenthe first component and the second component.
 10. The method of claim 6,wherein the second interstitial material is electrodeposited between thefirst component and the second component.
 11. The method of claim 6,wherein the second interstitial material is electrodeposited over thefirst component.
 12. The method of claim 6, further comprising removingthe sacrificial layer, wherein the removing of the sacrificial layercreates a sensing gap between the first component and the secondcomponent.
 13. The method of claim 12, wherein the sensing gap is acapacitive sensing gap between a resonator of a microscale sensingdevice and a sense electrode of the microscale sensing device, whereinthe resonator is configured to sense a change in resonant frequency. 14.The method of claim 12, wherein the sensing gap comprises aheight-to-width ratio of at least 100:1.
 15. A method for forming adevice, comprising: applying a catalyst to a substrate to create apattern on a substrate; initiating growth of carbon nanotubes from thecatalyst; at least partially coating to the carbon nanotubes with aceramic material, wherein: a thickness of the ceramic material issubstantially uniform; interstices between the carbon nanotubes remain;the carbon nanotubes have a height-to-width ratio of 100:1; and astrength of the carbon nanotubes is below a threshold level to withstandforces applied during a wet etching process; and interlocking the carbonnanotubes together by infiltrating the carbon nanotubes with a metalmaterial, wherein: the metal material at least partially fills theinterstices between the carbon nanotubes; and the interlocking of thecarbon nanotubes increases the strength of the carbon nanotubes abovethe threshold level to withstand the forces applied during the wetetching process.
 16. The method of claim 15, further comprising,infiltrating the interstices between the carbon nanotubes with ametallic material, wherein the infiltrating further increases thestrength of the carbon nanotubes above the threshold level to withstandthe forces applied during the wet etching process.
 17. The method ofclaim 16, wherein the infiltrating is performed by a nickel sulfamatebath or a nickel chloride bath.
 18. The method of claim 15, wherein theheight-to-width ratio is 200:1.
 19. The method claim 15, wherein theceramic material is silicon or silicon nitride.
 20. The method of claim15, wherein the uniform coating is applied by a pulsed current.